1. Field of the Invention
The present invention relates to a control apparatus of an EGR (exhaust gas recirculation) control valve.
2. Description of the Related Art
To reduce the amount of nitrogen oxide discharge in exhaust gas of an internal combustion engine, it is effective to restrain the combustion temperature through the exhaust gas recirculation (EGR) with which exhaust gas is circulated to the intake side. Hereafter, the exhaust gas recirculated to the intake side by the EGR is referred to as “EGR gas.”
For effective operation of the EGR, it is necessary that the EGR gas flows from the exhaust side toward the intake side without a back flow. Therefore, the pressure on the exhaust side needs to be higher than that on the intake side. With an internal combustion engine utilizing a supercharger, however, the pressure on the intake side becomes higher than that on the exhaust side. A technique to provide an EGR control valve in a passage for exhaust gas circulation, detect the EGR-gas pressure, and close the EGR control valve if a back flow occurs is disclosed in JP-A-2004-100508.